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In the past two decades, astronomers have made a truly revolutionary discovery:
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that the cosmos is not only expanding, but is doing so at an ever-faster rate.
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The discovery of the accelerated expansion of the Universe
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was awarded the 2011 Nobel Prize in Physics.
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This is the ESOcast!
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Cutting-edge science and life behind the scenes of ESO,
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the European Southern Observatory,
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exploring the ultimate frontier with our host Dr J, a.k.a. Dr Joe Liske.
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Hello and welcome to the ESOcast.
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In this episode,
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we’re going to find out how astronomers learned
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that the expansion of the Universe is speeding up
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and why this finding is so important not only for our understanding of the Cosmos,
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but in fact, for all of Physics.
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Now this discovery was awarded the 2011 Nobel Prize in Physics,
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and observations from ESO’s telescopes in Chile
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played a significant role in this breakthrough.
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The Universe we live in was created in the Big Bang some 13.7 billion years ago.
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Ever since then, the Universe has been expanding.
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And for decades,
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astronomers have wanted to learn more about the nature of this expansion.
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For a long time, there were two main ideas:
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Either the expansion would gradually slow down and would ultimately come to a halt
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— after which the Universe would start to contract towards a “Big Crunch”.
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Or that the Cosmos would continue to expand forever.
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But how could astronomers find out
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which of these models of the Universe is the correct one?
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Well, one of the simplest ways of doing this
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is to accurately measure distances to very faraway galaxies,
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and then to compare these measurements with the predictions from these models
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for these particular galaxies.
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The comparison between the measurements and the predictions tells us
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which of the models is the right one.
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But how does this work?
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How can astronomers precisely determine these huge distances across the Cosmos?
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Well, stellar explosions, or supernovae, play a key role here.
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Supernovae are rare cosmic events: They are exploding stars.
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There is a certain type of explosion, known as a Type Ia Supernova,
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which is ideal for measuring distances in the cosmos.
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These supernovae are very bright,
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which means they can be seen even in distant galaxies.
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And what’s more their intrinsic brightnesses are always the same,
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meaning that their distances can be inferred
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from how bright they appear to us from Earth.
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By the 1990s two separate research teams
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had begun to carefully observe these exploding stars.
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For their studies,
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astronomers partly used telescopes at ESO’s La Silla observatory in Chile.
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Observing extremely distant supernovae in the mid 1990s
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was extremely challenging and exciting.
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We at ESO used the 3.6-metre, the NTT and the 1.5-metre telescopes
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to observe these high-redshift supernovae
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discovered at the nearby Tololo Observatory.
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In those days, 15 years ago,
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we were actually counting literally every single photon,
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which is a beautiful experiment to be part of, because it was extremely challenging.
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The critical component of all of this is of course to realise
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that we did not set out to find the accelerating Universe,
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so watching a new paradigm in physics establish itself
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has of course been very interesting and it’s been great fun.
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Once we had established that the distant supernovae were too far away
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for a Universe that was dominated by gravity
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we had to go back and measure this again.
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So the accelerated expansion that we measured with the first set of supernovae
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was then translated very quickly into a new component for cosmology:
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dark energy,
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we had to confirm that result.
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What we did is we asked for VLT time like other groups as well
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to confirm what we had measured to get better data with a bigger telescope
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and to get a better sampling of the supernovae themselves.
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The discovery of the accelerating expansion of the Universe
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was one of the most unexpected and important of the last decades.
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It was so unexpected because up until that point,
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everyone believed that the expansion of the Universe should be slowed down
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by the attractive force of gravity exerted by all of the matter in the Universe.
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But, as it turns out, the Universe is in fact much more interesting than that.
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But why is this acceleration so important?
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Well, as far as we know, there are two possible explanations for the acceleration:
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The number one explanation is
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that nearly ¾ of the Universe consist of some form of this mysterious dark energy.
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Dark energy is so mysterious because it exerts negative pressure.
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That’s pretty exotic stuff.
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The number two explanation is
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that there is something wrong with our understanding of gravity.
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In other words, that Einstein’s theory of general relativity is not quite correct.
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In either of these cases,
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we are confronted with completely new physics,
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and that’s why this is so important
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and why this discovery was awarded the 2011 Nobel Prize in Physics.
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This is Dr J signing off for the ESOcast.
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Join me again next time for another cosmic adventure.
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ESOcast is produced by ESO, the European Southern Observatory.
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ESO, the European Southern Observatory,
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is the pre-eminent intergovernmental science and technology organisation in astronomy
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designing, constructing and operating the world’s most advanced ground-based telescopes.
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Transcription by ESO; translation by —
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Now that you've caught up with ESO,
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head 'out of this world' with Hubble.
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The Hubblecast highlights the latest discoveries
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of the world´s most recognized and prized space observatory,
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The NASA/ESA Hubble Space Telescope.